In the 90s, I was working a turn-around at a sister facility and learned the niftiest trick related to Double Block and Bleed (DB&B). When the isolation valves and the bleed valve were nearby (i.e., a couple of feet or less) of each other, they would use just a single lock to secure the isolation. They would use a LOTO cable to pass through all three (3) lockout devices, with the isolation valves CLOSED and the bleed OPEN, join the ends of the cable and apply a single lockout lock to the cable.
During a turnaround, when hundreds of LOTOs are performed daily, any means which reduces the number of locks needed to secure a LOTO is a welcomed practice. I have since mentioned this practice in almost all of my LOTO training sessions and have written about the practice many times. But over the past two weeks, I have worked with a key client on implementing their new LOTO program. This client is indeed well on its way to being “world-class” in safety, as it was a process engineer who questioned the practice I mentioned above.
This client is a PSM/RMP client, and they have come a long way in the past 12 years, such that the facilities are learning of Layers of Protection Analysis (LOPA) and Independent Layers of Protection (ILP). And it was in the LOPA where this process engineer learned of ILP. So he had an excellent question regarding this LOTO protection and its INTENDED LEVEL of Protection…
Does Double Block and Bleed require INDEPENDENT isolation?
And here is where I may have lost the debate and really began to question this practice.
NOTE: do not waste your time looking in 1910.147 or the LOTO CPL, as this discussion far surpasses any type of regulatory/compliance requirements.
OSHA’s definition of DB&B states:
Double block and bleed means the closure of a line, duct, or pipe by closing and locking or tagging two inline valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.
So the question is…
Does each valve in the DB&B arrangement require an INDEPENDENT LOTO, or can all three (3) valves be locked out with a cable and single lock?
NOTE: PLEASE also read my FREE article Lockout with cable/shark leader and identifying the isolation device is under LOTO control
If we use the ILP analogy, I have to say that EACH valve would have its OWN LOTO – hence, a single-point failure would not lessen the protection the DB&B arrangement is intended to provide.
If we use the cable, this method does NOT provide an ILP, as a single failure (e.g., the cable is cut, breaks, routed incorrectly, etc.), we have a total failure of the DB&B. We may still have single valve isolation, but we would no longer have the required level of isolation. In my August 2020 article (linked above) I wrote about the flaws when all we do is route the cable through a valve handle and provide no means to identify this as a LOTO/Isolation Point so it will not be tampered with.
What are your thoughts on using a single cable to secure ALL THREE (3) valves in a DB&B with a single chain/cable?